Compound Adjectives

This is a common mistake that I am coming across in ILIAS's English language files, so I thought it could do with a bit of explanation.

1 The Basic Rules

Whenever two or more words are combined to form a unit with a single meaning that then modifies a following noun, they become a compound adjective and need to be joined together using a hyphen. The following examples should give you a better understanding of this.

You will note in these examples that the hyphenated compound adjective is always before the noun. If it is not used in this position, then you don’t need hyphens. If you have a comma-separated list of adjectives and/or compound adjectives before a noun, then you still need to hyphenate compound adjectives as they still count as being before the noun, even if they are at the start of the list e.g. a hard-working, efficient employee.

        For example: Chris is incredibly good looking. Because ‘good looking’ isn’t modifying a following noun, it doesn’t need to be hyphenated.

The compound adjective itself doesn’t have to be made up only of adjectives. There are many different parts of speech that are regularly combined to make a compound adjective. These include among others:

In a sudden attack of dreams of grandeur, I will now launch my literary career...

The German-speaking employee with the ice-cold glare trudged across the burning-hot sands of the wind-etched, barren landscape, making long-term plans of revenge!

You will notice in this example sentence, that 'wind-etched' and 'barren' are separated by a comma - not joined together with a hyphen. That is because they are two separate modifying concepts. 'Wind-etched' tells that the landscape has been formed by the wind - probably sandstorms have carved the rocks into distinctive shapes. 'Barren' tells us that there is nothing growing there. No cacti or dense, thick, schrub-like vegatation clings to this soil. 'wind-etched' and 'barren' are telling us two different things about the landscape and therefore should be separated by a comma.

In the end it all comes down to clarity and 'what makes sense'. Take a look at this example, from an advertisment, written in title case. 

        Treat Yourself to a Walk in Bath

A quick search online reveals Bath to be a beautiful city and I ask myself why I have never walked around this gorgeous spa town before. I click enthusiastically on the link and.... discover that that the person who wrote the text made a mistake. What should have been written is this:

        Treat Yourself to a Walk-in Bath

Written this way, it becomes clear what is meant. 'Walk-in' becomes a single compound adjective (even though neither of the parts of speech is an adjective on its own, but rather a noun + a preposition) and means 'something that can be walked into', as opposed to having to climb into. A walk-in bath is a bath tub for people with limited mobility due to age or health issues, with a special sealed door for them to get in and out of the bath with ease. 

Wait another 20-30 years before you target me with that advertisement again guys!

Example from ILIAS:

Group Specific User Data. Written like this, this option could be read in two different ways. It could be read (as it is intended to be) to mean 'user data that is specific to the group'. It could, however, also be read to mean 'the specific user data should be grouped' - i.e. 'group' could be read as the imperative of the verb 'to group'. If written with a hyphen - Group-Specific User Data - it become clear that 'group' and 'specific' belong together and form a single compound adjective which modifies 'User Data'.

2 Numbers

Compound adjectives starting with a number or fractions always need hyphens.

This is also true for numbers between twenty-one and ninetynine - wherever they appear in a sentence

3 Adverbs

There is, of course, a very common exception to these rules. That is - you don't hyphenate an adverb followed by any other part of speech (or longer adjective compound). For example:

And, of course, there are exceptions to the exceptions.

'Well' is an adverb, but because it is also an adjective (meaning healthy) it needs a hyphen when being used in a compund adjective.

4 Final Exceptions

Over time certain compound adjectives become so well used together, that they become one word. Words such as teenager (used to be teen-ager), bulletproof (used to be bullet-proof) etc...

Also - there are compound ajectives that don't ever get hyphenated. For example, set phrase from other languages that don't use the same hyphenation rules as in English.

        On the weekends she does pro bono work.

'Pro bono' comes from the Latin phrase 'pro bono publico' (for the public good) and is therefore never hyphenated.